Best-practice Time Point Ontology for Event Calculus-based Temporal Reasoning.
Robert Schrag · 2012
We argue for time points with zero real-world duration as a best ontological practice in pointand intervalbased temporal representation and reasoning. We demonstrate anomalies that unavoidably arise in the event calculus when realworld time intervals corresponding to finest anticipated calendar units (e.g., days or seconds, per application granularity) are taken (naively or for implementation convenience) to be time “points.” Our approach to eliminating the undesirable anomalies admits durations of infinitesimal extent as the lower and/or upper bounds that may constrain two time points’ juxtaposition. Following Dean and McDermott, we exhibit axioms for temporal constraint propagation that generalize corresponding naive axioms by treating infinitesimals as orthogonal first-class quantities and we appeal to complex number arithmetic (supported by programming languages such as Lisp) for straightforward implementation. The resulting anomaly-free operation is critical to effective event calculus application in commonsense understanding applications, like machine reading.